Noise Suppression Capacitor

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aucklander

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#310663 10-Nov-2023 13:34

Hi all,

I have older style Black & Decker router which trips the RCD. I opened the line filter enclosure on the power cord and by the looks of it it appears the capacitor is blown? I cannot find exact replacement so I am looking to replace with a made-up assembly but I have issues in sourcing those individual capacitors as well...

I can get 2 capacitors 0.1microF each and use in series to give me the 0.05uF (for the Cx capacitor in the schematic). All for $6, so no issues there.

https://snw.nz/products/2-x-wima-mkp10-0-1uf-0-1%C2%B5f-100nf-630v-5-capacitor-ep046?_pos=1&_sid=c0d4889f2&_ss=r

But I cannot get the 2500pF (2.5nF) capacitors... any ideas please? I am after a solution where I can pick them ASAP, or this weekend.

Many thanks in advance.

Dynamic

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#3158027 10-Nov-2023 13:38

I'm not answering your specific question, but wonder if an old-school isolating transformer may work around the problem until you can get the components?

This sort of thing: ISOLATING TRANSFORMER | Trade Me Marketplace

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aucklander

477 posts

Ultimate Geek

#3158041 10-Nov-2023 14:14

those capacitors, from what I understand, also protect the motor (specifically the brushes). Without the capacitor there is way more sparks at the brushes, which will damage the motor quicker. They are not only to prevent electrical interference getting pushed back (up the power line). The explanation about the sparks, which I found on a woodworking forum, made sense to me as it explained what is happening everytime a brush disconnects then re-connects to the rotor...

aucklander

477 posts

Ultimate Geek

#3158043 10-Nov-2023 14:19

I wonder if something like this would work as a replacement for the complete assembly on the power cord?

https://www.jaycar.co.nz/240v-ac-emi-filter/p/MS4001?pos=3&queryId=2a1ce3ba74b8b258929878f8afeb2169&sort=relevance&searchText=emi

tweake

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#3158078 10-Nov-2023 15:29

aucklander:

I can get 2 capacitors 0.1microF each and use in series to give me the 0.05uF (for the Cx capacitor in the schematic). All for $6, so no issues there.

https://snw.nz/products/2-x-wima-mkp10-0-1uf-0-1%C2%B5f-100nf-630v-5-capacitor-ep046?_pos=1&_sid=c0d4889f2&_ss=r

But I cannot get the 2500pF (2.5nF) capacitors... any ideas please? I am after a solution where I can pick them ASAP, or this weekend.

Many thanks in advance.

the 2x 0.1uf caps look to be general purpose. your better off with the proper class caps. jacar has some 47uf x class caps.

the 2.5nf y class is looking a little trickier and they are the more critical ones.

SomeoneSomewhere

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#3158171 11-Nov-2023 09:41

Cx is directly across the mains. A failure to short circuit in these caps will result in a fire, so they should be Class X caps specifically rated to fail open.

Cy is similar - they sit between mains and ground or the user. Failure to short of these can result in a shock, so again, they need to be rated as Class Y.

Something like this should be fine - for EMI caps like these, value is not terribly important; they're usually only 20% precision anyway: https://nz.mouser.com/ProductDetail/Walsin/YU0AH222M090DAMD0B?qs=wUXugUrL1qwK7gBBIFqFGw%3D%3D

The various electronics vendors usually have very fast shipping.

Gordy7

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#3158239 11-Nov-2023 11:55

How about this all in one delta suppression safety capacitor?

https://nz.element14.com/kemet/pzb300mc21r30/cap-0-15-f-20-paper-radial/dp/1678910

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

SomeoneSomewhere

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#3158343 11-Nov-2023 14:44

Yeah, I'd be happy with that. 'Delta' is the word I was missing. They're certainly not very common any more as a single component.

0.1uF instead of 0.05uF for Cx is totally fine; it's straight across the mains so all it'll do is be a little bit of power factor correction - it should still be perfectly good at absorbing the HF from the brushes.

Cy being 2.2nF instead of 2.5nF is a total non-issue.

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Gordy7

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#3158375 11-Nov-2023 17:39

SomeoneSomewhere:

Yeah, I'd be happy with that. 'Delta' is the word I was missing. They're certainly not very common any more as a single component.

0.1uF instead of 0.05uF for Cx is totally fine; it's straight across the mains so all it'll do is be a little bit of power factor correction - it should still be perfectly good at absorbing the HF from the brushes.

Cy being 2.2nF instead of 2.5nF is a total non-issue.

The element14 option is probably not the cheapest.

Buying individual X and y caps would likely cost more and take up more space.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

SomeoneSomewhere

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#3158376 11-Nov-2023 17:56

Yeah, but for a device across the mains getting it from a reputable supplier is a good plan.

aucklander

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#3158451 12-Nov-2023 09:14

update: I got a proper 10A EMI filter from Jaycar ($17.90) and installed it as per the pictures, tried to use the old enclosure for the filter to support the cable ends and the new filter, made some adaptations too, used 2 coats of "liquid electrical tape" on all exposed connections and I will apply another coat today, then the whole thing will also get wrapped in strong duct tape for extra mechanical strength and waterproofing.What is left inside the old filter enclosure is only wiring connecting the new filter to the ends of the old cables.

I have started the router 3-4 times after connecting the new filter and it seems to work perfectly, I had to look very carefully at the brushes to see any sparks as it is really hard to see (I mean... there are very, very small sparks at the brushes, this is why it was hard to see initially).

I am still to start using it for extended periods of time and see how it performs but I am confident this is a decent repair. The filter is rated 10A and the router draws around 4A.

One of the pictures shows the old filter next the new one.

- old filter had Cx = 0.05microF and Cy = 2x 2500pF

- the new filter has Cx = 0.1micro F and Cy = 2x 3300pF, this is the best match I could find.

Interesting thing: the old capacitor has written on it "25/085/21" and exactly the same numbers are shown on the new filter - what do these mean? Anyway, this gave me confidence this new filter is a suitable replacement.

Gordy7

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#3158472 12-Nov-2023 09:58

The filter selected seems pretty good for your replacement and application.

I would have been inclined to have cut a rectangular hole (if possible) in one of the shells so that most of the filter and electrical connections were inside the original housing.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

SepticSceptic

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#3158750 12-Nov-2023 23:06

I'd be a bit worried about the sharp screw ends of the screws holding down your replacement capacitor.

They could pierce any mains wiring still inside the original casing.

Especially so if there is continuous movement of the tool, flexing the wiring inside against the screw tip and exposed thread.

SomeoneSomewhere

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#3158751 12-Nov-2023 23:10

The class X cap should also really be as close as possible to the motor to minimize parasitic inductance in the cable.

I don't like that amount of protection on live conductors on a machine tool.

Gordy7

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#3158752 12-Nov-2023 23:23

A further hindsight option would have been to remove the components from the a Jaycar filter and fit them to the router filter case.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.